Color gamut refers to the range of colors that can be reproduced by an imaging device. Various imaging devices present different color gamuts. For example, one imaging device may be able to reproduce a wider range of colors than another imaging device. Alternatively, one imaging device may be able to reproduce a wider range in one or more areas of color space. Gamut differences may arise between devices that operate in the same color space or different color spaces. For example, various cyan-magenta-yellow-black (CMYK) devices may yield different CMYK gamuts. Similarly, the gamuts associated with red-green-blue (RGB) and CMYK devices may be different from one another. Color image data is typically converted using color profiles, such as International Color Consortium (ICC) profiles, that define the colorimetric responses of different imaging devices.
Gamut differences require care in mapping color image data from one imaging device for output by another imaging device. Gamut differences can be particularly pronounced in the darker regions of an image. For example, two different imaging devices may have substantially different black points, i.e., the darkest color value that can be reproduced by a device. Black point compensation (BPC) is a technique that can be used in conjunction with relative colorimetric conversions of images to perform gamut mapping. The BPC technique ordinarily involves adjusting the black scaling of colorimetric values in XYZ or linear RGB space in order to map the black point of one system, such as RGB, to that of another system, such as CMYK. The tonal range of an image is determined by the number of intermediate gray values between the white point and black point of the image. Black point matching techniques evaluate source and destination black points and apply corrections to avoid undesirable visual effects.